S30 



MOSSES AND FERNS 



CHAP. 



ally two) roots formed arise secondarily, and quite independ- 

 ently of each other, from cells lying below the surface, and 

 covered with one or two layers of cells. These cells soon as- 

 sume a tetrahedral form, and become the apical cells of the pri- 

 mary roots. The branching of the roots, hke that of the stem, 

 is really monopodial, although apparently a true dichotomy. 

 The vascular bundle of the root is monarch (Fig. 305, B), 

 and does not show a distinct endodermis. The phloem sur- 

 rounds the xylem completely, but apparently sieve-tubes are 



Fig. 307. — Selaginella Kraussiana. Development of the microsporangium, radial sec- 

 tions. A-C, X500; D, X23S. The nuclei of the archesporial cells are shown. 

 L, The leaf subtending the sporangium. 



not developed opposite the protoxylem. The elements of the 

 bundle are in structure like those of the stem-bundles. 



The Sporangium (Goebel (16); Bower (15)) 



The development of the sporangium is much like that of Ly- 

 copodium, and has been studied by Goebel and Bower in 5. 

 spinosa, and by the latter in 6^. Martensii also. In S. Kraus- 

 siana (Fig. 307, A) a radial section of the young sporangium 

 shows a very regular arrangement of the cells, with a single 

 central archesporial cell (the nucleated cell of the figure). 

 This evidently has arisen from a hypodermal cell of the central 

 row, and from it is already cut off by a periclinal, an outer cell. 



